Process for removing hydrogen sulphide from gases



Patented Mar. 1, 1932 UNITED: STATES THEODOB, THORSSELL AND AUGUST KRISTENSSON, OF CASSEL, GERMANY PROCESS FOR REMOVING HWJROGEN SULPHIDE FROM GASES PATE OFFICE 1 No Drawing. Application filed September 7, 1928, Serial No. 304,6;2, and in em-sa September 16, 1927.

It has frequently been proposed to remove hydrogen sulphide from mixtures of gases with iron compounds.

The best known are the suggestions to use form during the absorption and can be obtained by simple filtration. On the contrary,

it has the disadvantage that the power of absorption of the hydrogen sulphide by the ferric chloride solution'is limited so that a state of equilibrium soon manifests itself. The occurrence of this state of equilibrium depends upon the concentration of the ferric chloride solution used. The stronger the solution is the smaller proportion of the salt takes part in the reaction, as shown by the following table:

Grins. per 100 gr. solution Before After reduction reduction recovery F 8C]: F6013 1101 I In order to obtain in some degree a good yield, it is thus necessary to work with very dilute solutions, which is a disadvantage for the practical procedure. Furthermore,the

- use of ferric chloride has the disadvantage that the oxidation of the ferrous chloride formed takes place fairly slowly.

The present invention which is preferabl carriedoutat a'temperature of 60 to 8056: may be conducted at atmospheric temperature and it consists in the useof a basic ferric salt in a ferric salt solution or suspension ;as an absorbing agent for hydrogen sulphide and treating the solutionof the corresponding ferrous salt with an oxidizing agent and V washing the gases in said iron salt solution I Such a suspension is obtained by oxidation of the corresponding ferroussaltin neutral or weak acidi'solution. Bythis means, for instance, a part of' the iron in ferrous chlo ride separates out as-a basic chloride during the :oxidation.-.

Nitric acid is used the present application as oxidizing agent in order to produce an absorbing liquid, which consists of a basic ferric salt suspendedin aferricsalt solution. Concentrated solutions are preferably used.

g If a solutionof'ferrous chloride is oxidized with nitric acid,then a pure,- bright yellow body suspended finely through the solution is obtained. The liquid consists of ferric chloride solution. The p'roportionbetween the contents of iron and chlorine in the suspended solid body corresponds to the formula: FeCl .6Fe(OH) thus to a very basic ferric chloride. This is so finely divided that itis almost in-the colloidal state, that is, itsettles out from the liquid extremely slowly. The liquid with the therein suspended basic chloride thus possesses properties which make it particularly suitable for the practical use as a feeding fluid for absorption towers. a r Thereaction can beexpressed by the following equation: a a I A The NO formed in this reaction is again convertedintolnitric acid in the usual way;

eNo+9o+3H.o=eHNo.

The liquid with the therein'suspended solid basic chloride absorbs hydrogen sulphide from the gas mixture according to the fol-. lowing equation:

18FeCl 98 1811 The reaction proceeds quantitatively and the product is a clear solution with pure sulo phur suspended in it. This has not the disadvantage which causes difliculties in working 7 when absorbing with ferricchloride, namely that the reaction issoon limited and is dependent upon the concentration of the solution. Further, it has not the disadvantage that the .sul hur separated is mixed with much Fe(O as is the case when washing the gas mixture with a suspension of Fe (OH); in alkaline solution.

After filtering off or centrifuging oif the pure sulphur,-:the clear ferrous chloride solution is again oxidized with the recovered nitric acid. i I l a 1 Example "One cubic'meter of a solution,'-which contains 100 kg; 'Fecl is oxidized with 16.6 kgxHNO at about From'this escape 7' .9 kg. "NO whic'h oxidized with air and absorbed inwater again yield 16.6kg. I'Il TO The-oxidized solution contains 78.2 kg. dissolved FeOl and "85.2 kg. suspended recner egomz; I

l' he solution is used for gas washing, when 13.4 kg. H S become absorbed an d 1226 kg.

phide from gases and simultaneously obtaining the sulphur, comprising preparing an iron salt solution with a basic ferric salt suspended therein by treating a ferrous chloride solution with nitric acid, washing the gases with the said iron salt solution and then treating the resulting solution of iron salt and hydrogen sulphide with an oxidizing agent to make it suitable for use again.

In testimony whereof we have signed our names to this specification.

THEODOR THORSSELL. j AUGUST KRISTENSSON.

Ssepa'rated. After filtering'thesulphur, the solutionconstitutes the aforesaid starting solution with 1OO kg. FeCl *Vhat we claim is: y

1. A process'for removing hydrogen sulnhide from gases and simultaneously obtaining the sulphur, comprising preparing an iron salt solu'tion with a-basic ferric salt sus- 45 .pendedrtherein by treating a ferrous chloride Gil act

the gases with the said iron saltso-lution and r then treating the resulting solution of iron salt and hydrogen sulphide :with an oxidizng-agent-tomake it suitable for use again;

4. A process forremovingz-hydrogen sul- 

